Apparatus for determining reactant purity

ABSTRACT

An apparatus ( 10 ) configured to determine reactant purity comprising: a first fuel cell ( 11 ) configured to generate electrical current from the electrochemical reaction between two reactants, having a first reactant inlet ( 13 ) configured to receive a test reactant comprising one of the two reactants from a first reactant source ( 7, 5, 16 ); a second fuel cell ( 12 ) configured to generate electrical current from the electrochemical reaction between the two reactants, having a second reactant inlet ( 14 ) configured to receive the test reactant from a second reactant source ( 5 ); a controller ( 20 ) configured to apply an electrical load to each fuel cell and determine an electrical output difference, OD t , between an electrical output of the first fuel cell ( 11 ) and an electrical output of the second fuel cell ( 12 ), and determine a difference between a predicted output difference and the determined electrical output difference, OD t , the predicted output difference determined based on a historical output of difference and a historical rate of change in said output difference determined at an earlier time, said controller ( 20 ) configured to provide a purity output indicative of the test reactant purity at least based on the difference between the predicted and determined output difference.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/312,250 filed Nov. 18, 2016, which is a National Phase entry ofInternational Application No. PCT/GB2015/051313, filed May 5, 2015,which claims priority to Great Britain Application No. 1408866.0, filedMay 19, 2014, the disclosures of which are incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus configured to determine thepurity of a reactant. In particular, it relates to an apparatus fordetermining the purity of a fuel, such as hydrogen, and/or an oxidant,such as air. It also relates to a filling station or stationary powerdevice including the apparatus and a method of determining reactantpurity.

The use of hydrogen as a fuel for the generation of electrical power infuel cells is becoming of increasing importance. Purity of the hydrogensupply is important for optimal electrical power generation and formaintaining fuel cells using that hydrogen in optimal condition.

Currently, hydrogen used in fuel cell systems is often synthesizedthrough the steam reforming of natural methane gas. Even where bestquality practices are used, a number of contaminants may be present inthe hydrogen fuel which are harmful to fuel cell operation. Although theharm is usually reversible, in the worst cases a high degree ofcontamination may be present including some compounds which may causeirreversible harm to the fuel cell.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, we provide an apparatusconfigured to determine reactant purity comprising;

a first fuel cell configured to generate electrical current from theelectrochemical reaction between two reactants, having a first reactantinlet configured to receive a test reactant comprising one of the tworeactants from a first reactant source;

a second fuel cell configured to generate electrical current from theelectrochemical reaction between the two reactants, having a secondreactant inlet configured to receive the test reactant from a secondreactant source;

a controller configured to apply an electrical load to each fuel celland determine an electrical output difference, OD_(t), between anelectrical output of the first fuel cell and an electrical output of thesecond fuel cell, and determine a difference between a predicted outputdifference and the determined electrical output difference, OD_(t), thepredicted output difference determined based on a historical outputdifference and a historical rate of change in said output differencedetermined at an earlier time,

said controller configured to provide a purity output indicative of thetest reactant purity at least based on the difference between thepredicted and determined output difference.

This is advantageous as it has been found that determining a predictionof what the output difference is going to be at a later time based onhistorical measurements and then, at the later time, determining theoutput difference and making a comparison provides an effective way ofdetermining or monitoring reactant purity. The historical values maycomprise a previously determined difference or rate of change or ahistorical average of the difference or rate of change.

The controller may be configured to determine at least three indicatorsat time t using two of the same indicators previously determined at anearlier time t−1, the indicators comprising a Delta_(t) indicatorrepresentative of the difference between a predicted output differenceand the determined output difference, a smoothed level indicator SL_(t),and a rate of change indicator ROC_(t), wherein;Delta_(t) =OD _(t)−(SL _(t-1) +Δt×ROC _(t-1))SL _(t)=(SL _(t-1) +Δt×ROC _(t-1))+α₁×Delta_(t)ROC _(t) =ROC _(t-1)+α₂×Delta_(t)and Δt comprises the time difference between time t and t−1, and α, andα₂ comprise predetermined values, wherein the purity output isdetermined using said indicators.

These indicators have been found to be effective at identifyingdeterioration of reactant quality over time, while being computationallyefficient.

The purity output may be determined using the electrical outputdifference, OD_(t).

The first reactant source may provide a reference reactant of the testreactant, the reference reactant having a known purity and the secondreactant source provides a fuel of an unknown purity. The first reactantsource may comprise a purification device, the purification deviceconfigured to purify part of the test reactant supplied from the secondreactant source.

Thus, the apparatus is configured to determine the electrical output oftwo fuel cells that are substantially identical other than the fuel thatis supplied to them. It may be assumed that the reference reactant ispure while the test reactant has an unknown purity which the presentapparatus may determine relative to the reference reactant.

Optionally the test reactant comprises a fuel. The fuel may comprisehydrogen. Optionally the test reactant comprises an oxidant, such asatmospheric air. The reactant may be for supply to a fuel cell powersource, such as a fuel cell powered vehicle or a stationary powerdevice.

The output difference may be determined based on an average of aplurality of sampled electrical output values from the first fuel celland the second fuel cell. Thus, a plurality of output values may beaveraged and the difference determined or a plurality of outputdifferences determined and then averaged. The average may comprise amodal, mean or median average, measure of central tendency or any otheraverage.

The controller may be configured to determine if the rate of changeindicator exceeds a predetermined threshold range and, if so, provide awarning of changing reactant purity. The controller may be configured todetermine if the smoothed level indicator exceeds a predeterminedthreshold range and, if so, provide an indication that the reactantpurity is unacceptable. The controller may be configured to determine ifthe Delta_(t) indicator exceeds a predetermined threshold range and, ifso, provide an indication that the reactant purity is unacceptable.Thus, the controller may only raise an alarm or warning if apredetermined threshold is exceeded. Alternatively, it may provide aplurality of warnings based on a plurality of thresholds.

The apparatus may include a third fuel cell configured to generateelectrical current from the electrochemical reaction between the tworeactants, wherein the test reactant comprises a first test reactant andthe other of the two reactants comprises a second test reactant;

the first fuel cell configured to receive the first test reactant fromthe first reactant source and the second test reactant from a fourthreactant source;

the second fuel cell configured to receive the first test reactant fromthe second reactant source and the second test reactant from the fourthreactant source;

the third fuel cell configured to receive the first test reactant fromthe first reactant source and the second test reactant from a thirdreactant source,

the controller configured to determine an electrical output difference,OD_(t), between an electrical output of the

first and second fuel cell;

first and third fuel cell; and

second and third fuel cell,

the controller configured to give an indication of the first testreactant purity and the second test reactant purity at least based on adifference between a predicted output difference and the determinedoutput difference, OD_(t), the predicted output difference determinedbased on a historical output difference and a historical rate of changein said output difference for each of the output differences.

The first test reactant may comprise a fuel and the second test reactantcomprises air; the first reactant source comprising a pure fuel source;the second reactant source comprising a fuel source of unknown purity;the third reactant source comprising a pure air source or an air sourceof unknown purity and the fourth reactant source comprising the other ofthe pure air source and air source of unknown purity.

The controller may be configured to output an indication of theperformance difference between the third fuel cell and the second fuelcell. Thus, the output difference between second and third fuel cellsmay provide an indication of fuel cell health.

The first fuel cell may comprise a plurality of series-connected fuelcells in a stack and/or in which the second fuel cell comprises aplurality of series-connected fuel cells in a stack.

According to a second aspect of the invention we provide a method fordetermining an indication of reactant purity comprising;

measuring an electrical output of a first fuel cell having a loadapplied thereto and configured to generate electrical current from theelectrochemical reaction between two reactants, one of the two reactantscomprising a test reactant supplied from a first reactant source to thefirst fuel cell;

measuring an electrical output of a second fuel cell having a loadapplied thereto and configured to generate electrical current from theelectrochemical reaction between the two reactants, the test reactantsupplied to the second fuel cell supplied from a second reactant source;

determining an electrical output difference, OD_(t), between anelectrical output of the first fuel cell and an electrical output of thesecond fuel cell,

providing an indication of the test reactant purity at least based on adifference between a predicted output difference and the determinedoutput difference, the predicted output difference determined based on ahistorical output difference and a historical rate of change in saidoutput difference.

The step of providing an indication may comprise;

determining at least three indicators at time t using two of the sameindicators previously determined at time t−1, the indicators comprisinga Delta_(t) indicator representative of the difference between apredicted output difference and the determined output difference, asmoothed level indicator SL_(t), and a rate of change indicator ROC_(t),wherein;Delta_(t) =OD _(t)−(SL _(t-1) +Δt×ROC _(t-1))SL _(t)=(SL _(t-1) +Δt×ROC _(t-1))+α₁×Delta_(t)ROC _(t) =ROC _(t-1)+α₂×Delta_(t)

and Δt comprises the time difference between time t and t−1, and α₁ andα₂ comprise predetermined values, wherein the method further comprisesproviding the indication of reactant purity using said indicators.

The method may comprise the step of providing the purity output,comprising an indication of test reactant purity, based on theelectrical output difference, OD_(t).

The step of determining the electrical output difference may comprisedetermining an average of a plurality of sampled electrical outputvalues from the first fuel cell and the second fuel cell and using saidaverage values to determine the electrical output difference.

The method may comprise determining if the rate of change indicatorexceeds a predetermined threshold range and, if so, provide a warning ofchanging reactant purity using said purity output. The method maycomprise determining if the smoothed level indicator exceeds apredetermined threshold range and, if so, provide an indication that thereactant purity is unacceptable using said purity output. The method maycomprise determining if the Delta_(t) indicator exceeds a predeterminedthreshold range and, if so, provide an indication that the reactantpurity is unacceptable.

The method may comprise the step of

measuring an electrical output of a third fuel cell having a loadapplied thereto and configured to generate electrical current from theelectrochemical reaction between two reactants, wherein the testreactant comprises a first test reactant and the other of the tworeactants comprises a second test reactant, the first fuel cellconfigured to receive the second test reactant from a third reactantsource, the second fuel cell is configured to receive the second testreactant from the third reactant source, and the third fuel cell isconfigured to receive the first test reactant from the first reactantsource and the second test reactant from a fourth reactant source,

the method further including the step of determining an electricaloutput difference, OD_(t), between an electrical output of the

first and second fuel cell

first and third fuel cell; and

second and third fuel cell, and

providing an indication of the first test reactant purity and the secondtest reactant purity using a difference between a predicted outputdifference and the determined output difference, the predicted outputdifference determined based on a historic output difference and ahistoric rate of change in said output difference for each of the outputdifferences.

According to a third aspect of the invention we provide a computerprogram or computer program product comprising code which, when executedby a processor causes an apparatus to perform the method of the secondaspect.

According to a fourth aspect of the invention we provide a reactantdistribution system configured to receive a reactant purity indicatorfrom each of a plurality of sensors located at geographically disparatereactant use locations and identify a location associated with each ofthe received indicators with reference to a reactant distributionnetwork configured to supply reactant to the reactant use locations, thesystem adapted to reconfigure the reactant distribution network and/ordisable the use of reactant at one or more reactant use locations inresponse to a received indicator that is representative of poor reactantpurity from a particular reactant use location based on the location ofsaid particular reactant use location in the reactant distributionnetwork.

The reactant use locations may comprise reactant dispensing locations,such as filling stations. Alternatively, the reactant use locations maycomprise stationary power devices that consume reactant suppliedthereto.

The system may be configured to reconfigure the reactant distributionnetwork by inhibiting the distribution of reactant to part of thereactant distribution network downstream of the dispensing location fromwhich the indicator of poor reactant purity is received. This preventsfurther reactant use locations from receiving poor purity reactant (ifit is assumed that the cause of the impurity is from the deliveredreactant). The downstream locations can be determined from thedistribution network.

The system may be configured to disable the use of reactant at one ormore reactant use locations by being configured to, using the reactantdistribution network, identify one or more reactant use locations thatreceived reactant from a common reactant source as the particularreactant use location and provide for the disablement of said identifiedreactant use locations. Thus, the reactant use locations can be stoppedfrom using or dispensing the poor quality reactant as the reactantdistribution network is used to determine which locations receivedreactant from the same source as the particular use location that hasthe poor reactant purity problem. Also, in the case of the reactant uselocation comprising a stationary power device, for example, each unitmay consume reactant at different rates. Therefore, by determining,automatically, which use locations, upstream or downstream, received thereactant from the same source provides an advantageous reactantdistribution network.

The system may be configured to provide a valve close signal, in realtime, for actuation of a valve in the reactant distribution network toprevent the flow of reactant along a distribution conduit downstream ofthe dispensing location from which the indicator of poor reactant purityis received.

The system may be configured to provide a signal, in real time, toprevent distribution of reactant from a batch of reactant to a reactantdispensing location(s) downstream along a predetermined route from thedispensing location from which the indicator of poor reactant purity isreceived and which also received reactant from said batch of reactant.

The system may be configured to provide an alternate supply signal toreconfigure the reactant distribution network such that the reactantdispensing locations located in the part of the reactant distributionnetwork downstream of the dispensing location from which the indicatorof poor reactant purity is received, are supplied with reactant from adifferent part of the network.

The alternate supply signal may comprise;

i) an instruction to open a valve in the reactant distribution networkto supply the affected reactant dispensing locations from an alternatepart of the network; or

ii) an instruction to dispatch a batch of reactant to one or more of thereactant dispensing locations located in the part of the reactantdistribution network downstream of the dispensing location from whichthe indicator of poor reactant purity is received;

iii) an instruction to divert a batch of reactant from its predeterminedroute to one or more of the reactant dispensing locations located in thepart of the reactant distribution network downstream of the dispensinglocation from which the indicator of poor reactant purity is received.

The system may be configured to provide an inhibition signal to one ormore of the identified reactant use locations to inhibit the use ofreactant received from the common source. Thus, the reactant uselocation may switch to a different reactant source, if present, or bedisabled until the reactant distribution network delivers reactant froma different source. Further, with reference to the distribution network,not only the reactant use location that generated the poor reactantpurity indication can be inhibited. This can prevent damage or thefurther distribution of poor quality reactant at other reactant uselocations.

According to a fifth aspect of the invention we provide a method orcomputer program or computer program product comprising code which, whenexecuted by a processor performs the steps of;

receiving a reactant purity indicator from each of a plurality ofsensors located at geographically disparate reactant use locations;

identifying a location associated with each of the received indicatorswith reference to a reactant distribution network configured to supplyreactant to the reactant use locations,

sending an instruction to reconfigure the reactant distribution networkand/or disable the use of reactant at one or more reactant use locationsin response to a received indicator that is representative of poorreactant purity from a particular reactant use location based on thelocation of said particular reactant use location in the reactantdistribution network.

DESCRIPTION OF THE DRAWINGS

There now follows, by way of example only, a detailed description of oneor more embodiments of the invention with reference to the accompanyingdrawings, in which;

FIG. 1 shows a schematic diagram of a first example apparatus utilisingtwo fuel cells and configured to determine the purity of a reactant;

FIGS. 2a to c show a series of graphs illustrating the variation ofseveral indicators of reactant purity over time for an example data set;

FIG. 3 shows a schematic diagram of a first example apparatus utilisingthree fuel cells and configured to determine the purity of tworeactants; and

FIG. 4 shows a reactant distribution system for reconfiguring a reactantdistribution network.

DETAILED DESCRIPTION OF THE INVENTION

An apparatus for determining reactant purity 10 is shown in FIG. 1. Theapparatus 10 has particular application for determining the purity of afuel, such as hydrogen. Accordingly, the apparatus 10 may form part of afuel filling station for fuel cell powered devices, such as vehicles.The apparatus may thus be configured to monitor the purity of the fuelstored or supplied to a filling station for contamination detection andcan assess fuel purity before it is delivered to customers. Theapparatus can also be used to monitor the hydrogen supply being fed toan operational or “primary” fuel cell being used as an electrical powersupply for a building or vehicle or communications infrastructure, forexample. The invention is also useful for determining reactant purityfor fuel cell based stationary power devices that provide power orbackup power for equipment such as mobile telecommunications masts. Theapparatus can be used as a periodic testing system or as an “in-line”,continuously-operating reactant/fuel monitor.

The apparatus may also determine the purity of other reactants, such asan oxidant. Fuel cells may utilise atmospheric air as the oxidant andaccordingly, the apparatus may be used to assess air purity. This isadvantageous, as the apparatus may be configured to provide informationon changes in fuel and/or air purity.

The apparatus uses a configuration of at least two fuel cells in orderto monitor reactant purity. An advantage of using fuel cells todetermine the reactant purity is that it is relatively inexpensivecompared to existing elemental analysis apparatus and methods. Anotheradvantage of a fuel cell based purity monitoring system is that, bytheir very nature, the fuel cells performing the purity monitoring canreadily be configured to be sensitive to exactly the same contaminantsthat are harmful to operation of a primary fuel cell stack with whichthe purity monitor can be associated.

FIG. 1 shows a schematic diagram illustrating the principles ofoperation of a first configuration of the apparatus 10. The puritymonitor 10 includes a first fuel cell 11 and a second fuel cell 12. Thefirst fuel cell 11 is a reference fuel cell and may further comprise anumber of individual fuel cells disposed in series-connectedconfiguration as a reference fuel cell stack 11. The second fuel cell 12is a test fuel cell and may further comprise a number of individual fuelcells disposed in series-connected configuration as a test fuel cellstack 12. The reference cell 11 has a fuel inlet 13 and the test cell 12has a fuel inlet 14. In this arrangement, the fuel inlets 13, 14 areboth supplied from a common hydrogen source 5. Hydrogen source 5 may beany form of hydrogen source including, but not limited to, any form ofstorage tank or vessel, a continuous piped supply, or a hydrogengenerator such as a steam reforming system. The fuel inlet 13 isconnected to the hydrogen source 5 by way of a purifier 16. Accordingly,the purifier 16 can be considered to be a source of pure hydrogen. Thepurifier 16 may be any form of filter capable of removing contaminantsthat would degrade the electrical performance of the reference fuel cell11 and the test fuel cell 12. For example, any form ofcatalyst-activated purifier could be used. A preferred purifier is apalladium membrane. The purifier 16 is preferably situated between theinlet 13 and the hydrogen source 5. Any suitable purifier or in-line gaspurification method may be used, such as those based on an adsorptionmethod using porous media or pressure swing adsorption. A range ofpossible hydrogen purifiers are commercially available, such as theMicro Torr® range from SAES Pure Gas Inc.

In other embodiments the inlet 13 may connect to a separate purehydrogen fuel source 7 (shown in dashed lines in FIG. 1) instead of thepurifier 16.

The fuel cells 11 and 12 comprise portable consumer fuel cell powersupplies that are configured to receive a replaceable source of fuel.The use of consumer units in the purity determination apparatus is costeffective and, given that such units may be mass produced, theytypically have good uniformity in their performance. Rather than receivethe fuel from a replaceable fuel source, the fuel cells 11 and 12 areconfigured to receive the supply from the fuel source 16 comprising thepurifier and the fuel source 5 respectively.

A calibration valve 31 enables both fuel cells 11 and 12 to be fed withthe same reactant, which in this embodiment is the purified or purehydrogen. The calibration valve 31 may be actuated such that the fuelcell 12 receives pure hydrogen via conduit 32. With the calibrationvalve 31 in this position the controller 20 may perform a calibrationprocedure in order to determine and calibrate out any systematicelectrical output differences between fuel cells 11 and 12 by suitablyadjusting controller 20. In normal use, the calibration valve 31 can beactuated such that the second fuel cell 12 receives hydrogen from source5 and the first fuel cell 11 receives hydrogen from source 7 or purifier16.

The first, reference fuel cell 11 has an electrical output 17 and thesecond, test fuel cell 12 has an electrical output 18. Both electricaloutputs 17, 18 are connected to a controller 20. The controller 20 isconfigured to apply an electrical load (not shown) to each of the fuelcells 11, 12 and to monitor the electrical outputs 17, 18 of the fuelcells 11, 12. The controller 20 is also configured to compare theelectrical outputs to determine an electrical output difference betweenthe fuel cells 11, 12. In this embodiment the electrical outputs 17, 18comprise USB outputs that connect, via a USB cable, to the controller20. The electrical output comprises a voltage. In particular, thecontroller may measure the fuel cell voltages at a constant outputcurrent. Alternatively, the controller may measure an output current ata constant voltage for each of the fuel cells 11, 12.

The controller 20 also provides a purity output 22 configured to give anindication of the fuel reactant purity of the hydrogen source 5 based onan output of the controller 20. In this embodiment, the purity output 22is in the form of a traffic light system. In particular, a green light23 shows that the fuel/reactant quality is acceptable withinpredetermined limits, an amber light 24 indicates a warning of changingreactant purity and a red light 25 indicates an unacceptable reactantpurity. It will be appreciated that other indicators may be used such asa display. The controller 20 further includes a wireless communicationelement represented by antenna 26 to transmit measurements or itsdetermination of reactant purity to another device. Thus, in anotherembodiment, the controller may comprise a data collection part connectedto the fuel cells and a data analysis part remote from the fuel cellsand connected to the data collection part via a communication linkconfigured to determine the reactant quality from the collected data.The functionality of the controller may be embodied as software executedon a processor which receives the output from fuel cells 11, 12.

In use, the first fuel cell 11 receives hydrogen fuel from the purifier16, which in turn receives the fuel from hydrogen source 5. The secondfuel cell 12 receives fuel directly from the hydrogen source withoutpurification. The hydrogen source 5 thus supplies the reactant to betested. The fuel inlet 13 and the fuel inlet 14 each connect to arespective pressure regulator 27, 28 to ensure that each fuel cell issupplied with fuel at the same rate. Both fuel cells 11, 12 receiveatmospheric air as the other reactant via air inlets 29, 30. The fuelcells 11, 12 are located side by side and therefore it is assumed thatthey both receive air of the same purity such that any difference intheir electrical output will be caused by the difference between thesupply of purified fuel to the first fuel cell 11 and the un-purifiedtest fuel to the second fuel cell 12.

The fuel cells 11, 12 generate electrical power and the controller isconfigured to periodically determine a difference, OD_(t), in theelectrical output between them. In particular, in this example, thecontroller is configured to sample the electrical output voltage eachsecond. Each minute, the controller is configured to take an average ofthe electrical output voltage over the previous 60 seconds and, usingthe average electrical output, determine an electrical output (voltage)difference. Thus, at time t, the controller determines an outputdifference OD_(t). The output difference of the preceding period isdesignated OD_(t-1).

The controller 20 is configured to predict what the output differenceOD_(t) is going to be based on a historic output difference and ahistoric rate of change in said output difference. For initialisation,the historic output difference and the historic rate of change may eachcomprise a predetermined value. Otherwise, the historic outputdifference and historic rate of change may be calculated at each timeinterval t. The historic output difference may comprise a previouslydetermined output difference and, likewise, the historic rate of changemay comprise a previously determined rate of change. The controller 20is then configured to determine a further difference between thepredicted output difference and the output difference OD_(t). Thecontroller may determine whether or not this further difference lieswithin predetermined a threshold or limits and, based on thisassessment, the controller may provide a purity output 22, which maycomprise an alert, value or warning that the reactant purity supplied tofuel cell 12 is changing or outside acceptable limits. In this example,such an alert indicates that the hydrogen purity from source 5 may bepoor.

In a further example, the controller is configured to give an indicationof reactant purity based on any one of at least three indicators orparameters determined at time t using two of the same indicatorspreviously determined at time t−1, namely SL_(t-1) and ROC_(t-1). Theindicators comprising a Delta_(t) indicator representative of thedifference between a predicted output difference and the determinedoutput difference as described above, a smoothed level indicator SL_(t),and a rate of change indicator ROC_(t), wherein;Delta_(t) =OD _(t)−(SL _(t-1) +Δt×ROC _(t-1))  (1)SL _(t)=(SL _(t-1) +Δt×ROC _(t-1))+α₁×Delta_(t)  (2)ROC _(t) =ROC _(t-1)+α₂×Delta_(t)  (3)Δt comprises the time difference between time t and t−1, and α₁ and α₂comprise predetermined values. α₁ and α₂ may comprise constants. α₁ andα₂ may be used to tune the sensitivity of the indicators to changes inthe other indicators. Further, α₁ and α₂ may be related such that;α₂=α₁ ²/((2-α₁)×Δt)  (4)Accordingly, equation 3 becomes;ROC _(t) =ROC _(t-1)+(α₁ ²/((2-α₁)×Δt))×Delta_(t)  (5)α₁ may be chosen between 0 and 1 to give a compromise between (a)smoothing out the noise in the observations (small α₁) and (b) allowingdiscrete features of the time series to be represented by the indicators(large α₁). Other relationships between α₁ and α₂ are possible. Forexample, α₂=α₁ ²/(2−α₁) is a possible relationship that may yieldadvantageous results.

The indicators Delta_(t), smoothed level indicator SL_(t), and rate ofchange indicator ROC_(t) may each have associated threshold levels orranges. The smoothed level indicator represents a historic outputdifference and the rate of change indicator represents a historic rateof change. Accordingly, when it is determined that any one of theindicators has exceeded or falls outside its predeterminedthreshold/range, the purity output 22, may be configured to generate analert.

In this embodiment, using the traffic light warning system, the Rate ofChange indicator is used to give an amber warning ahead of a red alert.Further, the Smoothed Level indicator and the Delta output are used togive a red alert if there is either a consistently high voltagedifference between the fuel cells 11, 12 or a sudden ‘spike’ or ‘jump’in the voltage difference between the fuel cells 11, 12.

FIGS. 2a to 2c show an example data set to demonstrate the changes inthe indicators and how they may be used to warn a user of possiblydeteriorating or poor reactant purity.

FIG. 2a shows the voltage output difference 200 between fuel cell 11 andfuel cell 12. Initially, the output difference is within its associatedthreshold 201 and the green light 23 is illuminated to show the userthat the fuel purity is acceptable. It can be seen that the outputdifference value crosses a threshold value of 0.1 Volts afterapproximately 93 minutes from when monitoring started. This provides anindication that the fuel purity may have fallen below an acceptablelimit. Accordingly, the red light 25 is illuminated.

FIG. 2b shows a plot of the Rate of Change indicator ROC_(t) labelled212. The Rate of Change indicator has an associated threshold rangebetween +0.001 and −0.001 and labelled 210, 211. The range is exceededafter approximately 50 minutes. The controller is configured to use theRate of Change indicator exceeding its threshold range as a warning to auser rather than an alert that the purity level has fallen below anacceptable limit. Thus, after 50 minutes, an amber alert is raised andthe amber light 24 is illuminated. The ROC_(t) indicator has been foundto advantageously provide advance warning of changing reactant purityand a useful early warning of purity levels potentially decreasing belowacceptable levels.

FIG. 2c shows the Delta_(t) indicator 222. The delta_(t) value has anassociated threshold range 220, 221, which, in this example comprises−0.005 to +0.005. The delta_(t) value exceeds the threshold range at 102minutes from when monitoring began. Accordingly, the red light 25 isilluminated by the controller.

It will be appreciated that the threshold values and ranges may beselected depending on the application. Further, the predeterminedconstants, α₁ and α₂, may be tuned to the particular application.

FIG. 3 shows a second embodiment which may be used to determine thepurity of more than one of the reactants. In this embodiment, the samereference numerals have been used for identical features. Thisembodiment comprises a third fuel cell 33 which is identical inconstruction to the first and second fuel cells 11, 12. Rather thanreceive its fuel from the purifier 16, the first fuel cell 11 receivesfuel from a separate, pure source 7, although this is not a requirementwhen the three (or more) fuel cells 11, 12, 33 are provided. The thirdfuel cell is configured to receive its supply of fuel from the pure fuelsource 7. While the first and second fuel cells 11, 12 draw in the otherof their reactants (air) from the atmosphere via vents 29, 30, the thirdfuel cell 33 receives air from a purified air source 34. The purifiedair source may be an air purification device and/or filter or air from astorage vessel. The third fuel cell 33 includes an electrical output 35which connects to the controller 20.

The controller 20 is configured to apply a load and sample theelectrical output of the third fuel cell 33 as is performed for thefirst and second fuel cell. In addition to the electrical outputdifference OD_(t), which is determined from the difference betweenelectrical output of the first fuel cell and second fuel cell 12, thecontroller is also configured to determine the output difference OD_(t)between the first and third fuel cells 11, 33. Considering the first andthird fuel cells, they receive the same purity of fuel but the thirdfuel cell 33 acts as a reference for the purity of the air and the firstfuel cell receives the “test”, atmospheric air. Thus, the difference inelectrical output between the first and third fuel cells 11, 33 is(substantially) due to differences in air purity.

The controller may alternatively or in addition be configured todetermine the output difference between the second and third fuel cells12, 33. Considering the second and third fuel cells, they receive(potentially) different purity of fuel and (potentially) differentpurity of air. However, the third fuel cell 33, given that it receivespure air and pure fuel will not be contaminated in use. Thus, thedifference in electrical output between the second and third fuel cells12, 33 is (substantially) due to degradation of the second fuel cell 12due to contamination during use. Thus, the electrical output differencebetween the second and third fuel cells is advantageous and can beanalysed using the indicators discussed above.

The purity output 22 traffic light display is replaced by the generationof a report (not shown) that may be reported to the filling stationand/or a distribution network controller.

In a further embodiment, a fourth fuel cell may be provided whichreceives its hydrogen fuel form source 5 and its air supply from thepure air source 34. Thus, the apparatus is as shown in the table below.

Third Reactant Fourth Reactant Source Source (Pure Air) (Atmosphericair) First Reactant Source Third fuel cell First fuel cell (Pure H₂)Second Reactant Source Fourth fuel cell Second Fuel cell (Unknown purityH₂)

An output difference between the first and second fuel cells and thedifference between the third and fourth fuel cells provides twodeterminations of fuel purity. An output difference between the firstand third fuel cells and the difference between the second and fourthfuel cells provides two determinations of air (or other oxidant) purity.This may provide more reliable determinations.

A reactant distribution system may utilise the purity output 22 toconfigure a reactant distribution network. FIG. 4 shows a reactantdistribution network 40 which, in this example, comprises a hydrogendistribution network for delivering fuel to a plurality of reactant uselocations 41 a-f. The reactant use locations 41 a-f may comprisedispensing locations, such as hydrogen filling stations at which usersof fuel cell powered vehicles may fill their vehicle with hydrogen fuel.Each reactant use location includes a reactant purity sensor, which maycomprise the apparatus 10 described above, although any appropriatepurity sensor may be used.

The network 40 receives its supply of hydrogen fuel from a first networksource 42 and a second network source 43. The network sources maycomprise hydrogen generation plants or bulk storage depots.

The network 40 comprises a plurality of pathways 44 a-e and 45 a-d whichconnect the network sources 42, 43 with the dispensing locations 41 a-f.The pathways, in this example, comprise conduit along which the fuel mayflow. However, it will be appreciated, that the pathways 44 a-e and 45a-d may comprise segments of a predetermined delivery route of areactant delivery vehicle. In this example, the network 40 comprises afirst part supplied by the first network source 42 comprising locations41 a, 41 b, 41 d, 41 f and 41 e. These locations are suppliedsequentially via the pathways 44 a-e. The network 40 further comprises asecond part supplied by the second network source 43 comprisinglocations 41 c, 41 d, 41 f and 41 e. Locations 41 c, 41 d, 41 f aresupplied sequentially via the pathways 45 a, 45 b and 45 c. Location 41e is supplied directly from the second network source 43 via pathway 45d.

Each pathway 44 a-e, 45 a-d includes a valve 46, which can be actuatedto prevent flow along it. Thus, actuation of the valve 46 of pathway 44c will prevent fuel from the first network source 42 reaching downstreamlocations comprising 41 d, 41 f and 41 e.

The system may include a controller 47 which receives the output of thesensors at each location 41 a-f and can control the valves 46. This maybe performed by wireless communication or otherwise.

In a first example the valves of pathways 45 b, 45 c and 45 d areclosed. Thus, locations 41 a, 41 b, 41 d, 41 f, 41 e sequentiallyreceive fuel from the first network source 42. Location 41 c receivesfuel from the second network source 43.

In use, a poor reactant quality indicator may be received from thesensor at location 41 b. The controller 47 may be configured to locatethe sensor in the network 40 and thus identify that pathway 44 c isdownstream of location 41 b. Accordingly, to prevent the poor purityfuel from reaching further dispensing locations, namely, locations 41 d,41 f and 41 e, the controller may thus automatically issue a signal tocause the actuation of the valve 46 of pathway 44 c. There may be asource of contamination in the network around location 41 b.Accordingly, dispensing locations 41 d, 41 f and 41 e are isolated fromthe first network source 42 and the part of the network between source42 and valve 46 of pathway 44 c. The controller 47 may use furthersignals to further valves of further downstream pathways to actuate themto prevent the distribution of poor purity fuel.

Alternatively or in addition, the controller 47 may provide inhibitionsignals to use locations 41 b, 41 d, 41 f and 41 e to stop them using ordispensing fuel. This is advantageous as it prevents potentiallycontaminated fuel being dispensed into user's vehicles.

It will be appreciated that the valve 46 of pathway 44 c may, in analternate embodiment, represent the receipt of a signal in a fueldelivery vehicle to control the route followed by the vehicle. Thus, thevehicle may have been scheduled to deliver to the locations 41 a, 41 b,41 d, 41 f and 41 e in sequence. Thus, the signal may instruct thedelivery vehicle, in real time, to change its route so as not to deliverto the downstream locations 41 d, 41 f and 41 e.

The controller 47 may also issue an alternate supply signal to causefurther reconfiguration of the network 40 such that dispensing locationsaffected by the closure of the valve 46 of pathway 44 c can be suppliedfrom a different source, such as the second source 43. Thus, thealternate supply signal is configured to cause the actuation of thevalves 46 of pathways 45 b, 45 c and 45 d such that the pathways areopen to the flow of fuel from the second source 43. Accordingly, thedispensing locations 41 d and 41 f, isolated from the first networksource 42 are now supplied with fuel from the second network source 43.Further, the dispensing location 41 e is supplied directly from thesecond network source 43 rather than the first network source 42.

In an alternative embodiment, the alternate supply signal may define aroute for a fuel supply vehicle or tanker from the second network source43 to supply the affected dispensing locations. The alternate supplysignal may define a modification to a pre-existing route of a fuelsupply vehicle. Thus, valve 46 of pathway 45 b may, in this alternateembodiment, rather than represent a valve, represent the receipt of aninstruction for a fuel delivery vehicle to modify its intended route(which may be back to second network source 43) and instead continue todispensing location 41 d and 41 f. A further vehicle may be sent aninstruction to proceed to dispensing location 41 e. Thus, the controller47 can perform real-time reconfiguration of the routes followed by oneof, or a fleet of, fuel supply vehicles, in the same way valves in aphysical supply conduit infrastructure control the flow of fueltherealong. The signal from the controller 47 may generate an alert inthe delivery vehicle and provide a message to the driver to change theroute. Alternatively, the signal may provide instructions toautomatically reconfigure a navigation guidance apparatus, such as a GPSguidance device, with a new route for the driver to follow.

In a further embodiment, filtration apparatus may be actuated in thenetwork such that the network is reconfigured by way of a portion of thenetwork receiving filtered reactant. The filtration apparatus may belocated between dispensing locations and may be alongside any valves orprovided instead of a valve. Thus, filtration apparatus may be actuatedupstream and/or downstream of a dispensing location that reports poorreactant quality.

In a further embodiment, the reactant use locations 41 a-f comprisestationary power devices such as for supplying backup power to mobiletelecommunication masts. As the reactant use locations 41 a-f providebackup power they may only be activated periodically and some morefrequently than others. In this embodiment, the controller 47 isconfigured to use the distribution network to determine which reactantuse locations received reactant from the same source 42, 43. Thus, itmay consider reactant use locations downstream of an affected reactantuse location and upstream. This is because, even though an upstreamlocation may have received the potentially contaminated fuel before alocation that has reported poor reactant purity, it may not have beenactive and thus the contaminated fuel may be stored at the upstreamstationary power device ready for use. Accordingly, the controller 47may provide an inhibition signal to the reactant use locations thatreceived fuel from a common source. Alternatively, or in addition, thecontroller may reconfigure the distribution network such that new fuelis delivered to the affected reactant use locations 41 a-f, possiblyfrom a different source. The controller 47 therefore ensures anefficient network of reactant use locations.

The reactant distribution system may provide real-time information to auser of reactant purity at the fuel dispensing locations and any otherlocation in the network. Thus, a user can see the reactant purity ateach of the fuel dispensing locations in real time. This may comprise anaspect of the invention.

The invention claimed is:
 1. A reactant distribution method comprising:a reactant distribution system configured to receive a reactant purityindicator from each of a plurality of sensors located at geographicallydisparate reactant use locations; a location associated with eachindicator from each of the plurality of sensors with reference to areactant distribution network configured to supply reactant to thereactant use locations; the reactant distribution system adapted toreconfigure the reactant distribution network and/or disable the use ofreactant at one or more reactant use locations in response to a receivedindicator that is representative of poor reactant purity from aparticular reactant use location based on the location of saidparticular reactant use location in the reactant distribution network;and a controller configured to determine an electrical outputdifference, OD_(t), between an electrical output of a first fuel celland an electrical output of a second fuel cell, and determine adifference between a predicted output difference and the determinedelectrical output difference, OD_(t), the predicted output differencedetermined based on a historical output difference and a historical rateof change in the output difference determined at an earlier time, andthe controller configured to provide the reactant purity indicator fromeach of the plurality of sensors based on the difference between thepredicted and determined output difference.
 2. The method according toclaim 1, wherein the reactant distribution system is configured toreconfigure the reactant distribution network by inhibiting thedistribution of reactant to part of the reactant distribution networkdownstream of a dispensing location from which the reactant purityindicator of poor reactant purity is received.
 3. The method accordingto claim 2, wherein the reactant distribution system is configured toprovide a valve close signal, in real time, for actuation of a valve inthe reactant distribution network to prevent a flow of reactant along adistribution conduit downstream of the dispensing location from whichthe reactant purity indicator of poor reactant purity is received. 4.The method according to claim 2, wherein the reactant distributionsystem is configured to provide a signal, in real time, to preventdistribution of reactant from a batch of reactant to a reactantdispensing location(s) downstream along a predetermined route from thedispensing location from which the reactant purity indicator of poorreactant purity is received and which also received reactant from saidbatch of reactant.
 5. The method according to claim 1, wherein thereactant distribution system is configured to disable the use ofreactant at one or more reactant use locations by being configured to,using the reactant distribution network, identify one or more reactantuse locations that received reactant from a common reactant source asthe particular reactant use location and provide for the disablement ofsaid identified reactant use locations.
 6. The method according to claim5, wherein the reactant distribution system is configured to provide aninhibition signal to one or more of the identified reactant uselocations to inhibit the use of reactant received from the commonreactant source.
 7. The method according to claim 2, wherein thereactant distribution system is configured to provide an alternatesupply signal to reconfigure the reactant distribution network such thatthe reactant dispensing locations located in the part of the reactantdistribution network downstream of the dispensing location from whichthe reactant purity indicator of poor reactant purity is received and/orthe identified reactant use locations, are supplied with reactant from adifferent part of the reactant distribution network.
 8. The methodaccording to claim 7, the method wherein the controller is configured toprovide a purity output indicative of a test reactant purity at leastbased on a difference between a predicted test reactant output anddetermined test reactant output difference.